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The Osmiae


February has its sunny days, heralding spring, to which rude winter

will reluctantly yield place. In snug corners, among the rocks, the

great spurge of our district, the characias of the Greeks, the jusclo

of the Provencals, begins to lift its drooping inflorescence and

discreetly opens a few sombre flowers. Here the first midges of the

year will come to slake their thirst. By the time that
he tip of the

stalks reaches the perpendicular, the worst of the cold weather will be


Another eager one, the almond-tree, risking the loss of its fruit,

hastens to echo these preludes to the festival of the sun, preludes

which are too often treacherous. A few days of soft skies and it

becomes a glorious dome of white flowers, each twinkling with a roseate

eye. The country, which still lacks green, seems dotted everywhere with

white-satin pavilions. 'Twould be a callous heart indeed that could

resist the magic of this awakening.

The insect nation is represented at these rites by a few of its more

zealous members. There is first of all the Honey-bee, the sworn enemy

of strikes, who profits by the least lull of winter to find out if some

rosemary or other is not beginning to open somewhere near the hive. The

droning of the busy swarms fills the flowery vault, while a snow of

petals falls softly to the foot of the tree.

Together with the population of harvesters there mingles another, less

numerous, of mere drinkers, whose nesting-time has not yet begun. This

is the colony of the Osmiae, those exceedingly pretty solitary bees,

with their copper-coloured skin and bright-red fleece. Two species have

come hurrying up to take part in the joys of the almond-tree: first,

the Horned Osmia, clad in black velvet on the head and breast, with red

velvet on the abdomen; and, a little later, the Three-horned Osmia,

whose livery must be red and red only. These are the first delegates

despatched by the pollen-gleaners to ascertain the state of the season

and attend the festival of the early blooms.

'Tis but a moment since they burst their cocoon, the winter abode: they

have left their retreats in the crevices of the old walls; should the

north wind blow and set the almond-tree shivering, they will hasten to

return to them. Hail to you, O my dear Osmiae, who yearly, from the far

end of the harmas, opposite snow-capped Ventoux (A mountain in the

Provencal Alps, near Carpentras and Serignan 6,271 feet.--Translator's

Note.), bring me the first tidings of the awakening of the insect

world! I am one of your friends; let us talk about you a little.

Most of the Osmiae of my region do not themselves prepare the dwelling

destined for the laying. They want ready-made lodgings, such as the old

cells and old galleries of Anthophorae and Chalicodomae. If these

favourite haunts are lacking, then a hiding-place in the wall, a round

hole in some bit of wood, the tube of a reed, the spiral of a dead

Snail under a heap of stones are adopted, according to the tastes of

the several species. The retreat selected is divided into chambers by

partition-walls, after which the entrance to the dwelling receives a

massive seal. That is the sum-total of the building done.

For this plasterer's rather than mason's work, the Horned and the

Three-horned Osmia employ soft earth. This material is a sort of dried

mud, which turns to pap on the addition of a drop of water. The two

Osmiae limit themselves to gathering natural soaked earth, mud in

short, which they allow to dry without any special preparation on their

part; and so they need deep and well-sheltered retreats, into which the

rain cannot penetrate, or the work would fall to pieces.

Latreille's Osmia uses different materials for her partitions and her

doors. She chews the leaves of some mucilaginous plant, some mallow

perhaps, and then prepares a sort of green putty with which she builds

her partitions and finally closes the entrance to the dwelling. When

she settles in the spacious cells of the Masked Anthophora (Anthophora

personata, Illig.), the entrance to the gallery, which is wide enough

to admit a man's finger, is closed with a voluminous plug of this

vegetable paste. On the earthy banks, hardened by the sun, the home is

then betrayed by the gaudy colour of the lid. It is as though the

authorities had closed the door and affixed to it their great seals of

green wax.

So far then as their building-materials are concerned, the Osmiae whom

I have been able to observe are divided into two classes: one building

compartments with mud, the other with a green-tinted vegetable putty.

To the latter belongs Latreille's Osmia. The first section includes the

Horned Osmia and the Three-horned Osmia, both so remarkable for the

horny tubercles on their faces.

The great reed of the south, Arundo donax, is often used, in the

country, for making rough garden-shelters against the mistral or just

for fences. These reeds, the ends of which are chopped off to make them

all the same length, are planted perpendicularly in the earth. I have

often explored them in the hope of finding Osmia-nests. My search has

very seldom succeeded. The failure is easily explained. The partitions

and the closing-plug of the Horned and of the Three-horned Osmia are

made, as we have seen, of a sort of mud which water instantly reduces

to pap. With the upright position of the reeds, the stopper of the

opening would receive the rain and would become diluted; the ceilings

of the storeys would fall in and the family would perish by drowning.

Therefore the Osmia, who knew of these drawbacks before I did, refuses

the reeds when they are placed perpendicularly.

The same reed is used for a second purpose. We make canisses of it,

that is to say, hurdles, which, in spring, serve for the rearing of

Silkworms and, in autumn, for the drying of figs. At the end of April

and during May, which is the time when the Osmiae work, the canisses

are indoors, in the Silkworm nurseries, where the Bee cannot take

possession of them; in autumn, they are outside, exposing their layers

of figs and peeled peaches to the sun; but by that time the Osmiae have

long disappeared. If, however, during the spring, an old, disused

hurdle is left out of doors, in a horizontal position, the Three-horned

Osmia often takes possession of it and makes use of the two ends, where

the reeds lie truncated and open.

There are other quarters that suit the Three-horned Osmia, who is not

particular, it seems to me, and will make shift with any hiding-place,

so long as it have the requisite conditions of diameter, solidity,

sanitation and kindly darkness. The most original dwellings that I know

her to occupy are disused Snail-shells, especially the house of the

Common Snail (Helix aspersa). Let us go to the slope of the hills thick

with olive-trees and inspect the little supporting-walls which are

built of dry stones and face the south. In the crevices of this

insecure masonry we shall reap a harvest of old Snail-shells, plugged

with earth right up to the orifice. The family of the Three-horned

Osmia is settled in the spiral of those shells, which is subdivided

into chambers by mud partitions.

The Three-pronged Osmia (O. Tridentata, Duf. and Per.) alone creates a

home of her own, digging herself a channel with her mandibles in dry

bramble and sometimes in danewort.

The Osmia loves mystery. She wants a dark retreat, hidden from the eye.

I would like, nevertheless, to watch her in the privacy of her home and

to witness her work with the same facility as if she were nest-building

in the open air. Perhaps there are some interesting characteristics to

be picked up in the depths of her retreats. It remains to be seen

whether my wish can be realized.

When studying the insect's mental capacity, especially its very

retentive memory for places, I was led to ask myself whether it would

not be possible to make a suitably-chosen Bee build in any place that I

wished, even in my study. And I wanted, for an experiment of this sort,

not an individual but a numerous colony. My preference lent towards the

Three-horned Osmia, who is very plentiful in my neighbourhood, where,

together with Latreille's Osmia, she frequents in particular the

monstrous nests of the Chalicodoma of the Sheds. I therefore thought

out a scheme for making the Three-horned Osmia accept my study as her

settlement and build her nest in glass tubes, through which I could

easily watch the progress. To these crystal galleries, which might well

inspire a certain distrust, were to be added more natural retreats:

reeds of every length and thickness and disused Chalicodoma-nests taken

from among the biggest and the smallest. A scheme like this sounds mad.

I admit it, while mentioning that perhaps none ever succeeded so well

with me. We shall see as much presently.

My method is extremely simple. All I ask is that the birth of my

insects, that is to say, their first seeing the light, their emerging

from the cocoon, should take place on the spot where I propose to make

them settle. Here there must be retreats of no matter what nature, but

of a shape similar to that in which the Osmia delights. The first

impressions of sight, which are the most long-lived of any, shall bring

back my insects to the place of their birth. And not only will the

Osmiae return, through the always open windows, but they will also

nidify on the natal spot, if they find something like the necessary


And so, all through the winter, I collect Osmia-cocoons picked up in

the nests of the Mason-bee of the Sheds; I go to Carpentras to glean a

more plentiful supply in the nests of the Anthophora. I spread out my

stock in a large open box on a table which receives a bright diffused

light but not the direct rays of the sun. The table stands between two

windows facing south and overlooking the garden. When the moment of

hatching comes, those two windows will always remain open to give the

swarm entire liberty to go in and out as it pleases. The glass tubes

and reed-stumps are laid here and there, in fine disorder, close to the

heaps of cocoons and all in a horizontal position, for the Osmia will

have nothing to do with upright reeds. Although such a precaution is

not indispensable, I take care to place some cocoons in each cylinder.

The hatching of some of the Osmiae will therefore take place under

cover of the galleries destined to be the building-yard later; and the

site will be all the more deeply impressed on their memory. When I have

made these comprehensive arrangements, there is nothing more to be

done; and I wait patiently for the building-season to open.

My Osmiae leave their cocoons in the second half of April. Under the

immediate rays of the sun, in well-sheltered nooks, the hatching would

occur a month earlier, as we can see from the mixed population of the

snowy almond-tree. The constant shade in my study has delayed the

awakening, without, however, making any change in the nesting-period,

which synchronizes with the flowering of the thyme. We now have, around

my working-table, my books, my jars and my various appliances, a

buzzing crowd that goes in and out of the windows at every moment. I

enjoin the household henceforth not to touch a thing in the insects'

laboratory, to do no more sweeping, no more dusting. They might disturb

a swarm and make it think that my hospitality was not to be trusted.

During four or five weeks I witness the work of a number of Osmiae

which is much too large to allow my watching their individual

operations. I content myself with a few, whom I mark with

different-coloured spots to distinguish them; and I take no notice of

the others, whose finished work will have my attention later.

The first to appear are the males. If the sun is bright, they flutter

around the heap of tubes as if to take careful note of the locality;

blows are exchanged and the rival swains indulge in mild skirmishing on

the floor, then shake the dust off their wings. They fly assiduously

from tube to tube, placing their heads in the orifices to see if some

female will at last make up her mind to emerge.

One does, in point of fact. She is covered with dust and has the

disordered toilet that is inseparable from the hard work of the

deliverance. A lover has seen her, so has a second, likewise a third.

All crowd round her. The lady responds to their advances by clashing

her mandibles, which open and shut rapidly, several times in

succession. The suitors forthwith fall back; and they also, no doubt to

keep up their dignity, execute savage mandibular grimaces. Then the

beauty retires into the arbour and her wooers resume their places on

the threshold. A fresh appearance of the female, who repeats the play

with her jaws; a fresh retreat of the males, who do the best they can

to flourish their own pincers. The Osmiae have a strange way of

declaring their passion: with that fearsome gnashing of their

mandibles, the lovers look as though they meant to devour each other.

It suggests the thumps affected by our yokels in their moments of


The ingenuous idyll is soon over. The females, who grow more numerous

from day to day, inspect the premises; they buzz outside the glass

galleries and the reed dwellings; they go in, stay for a while, come

out, go in again and then fly away briskly into the garden. They

return, first one, then another. They halt outside, in the sun, or on

the shutters fastened back against the wall; they hover in the

window-recess, come inside, go to the reeds and give a glance at them,

only to set off again and to return soon after. Thus do they learn to

know their home, thus do they fix their birthplace in their memory. The

village of our childhood is always a cherished spot, never to be

effaced from our recollection. The Osmia's life endures for a month;

and she acquires a lasting remembrance of her hamlet in a couple of

days. 'Twas there that she was born; 'twas there that she loved; 'tis

there that she will return. Dulces reminiscitur Argos.

(Now falling by another's wound, his eyes

He casts to heaven, on Argos thinks and dies.

--"Aeneid" Book 10, Dryden's translation.)

At last each has made her choice. The work of construction begins; and

my expectations are fulfilled far beyond my wishes. The Osmiae build

nests in all the retreats which I have placed at their disposal. And

now, O my Osmiae, I leave you a free field!

The work begins with a thorough spring-cleaning of the home. Remnants

of cocoons, dirt consisting of spoilt honey, bits of plaster from

broken partitions, remains of dried Mollusc at the bottom of a shell:

these and much other insanitary refuse must first of all disappear.

Violently the Osmia tugs at the offending object and tears it out; and

then off she goes in a desperate hurry, to dispose of it far away from

the study. They are all alike, these ardent sweepers: in their

excessive zeal, they fear lest they should block up the speck of dust

which they might drop in front of the new house. The glass tubes, which

I myself have rinsed under the tap, are not exempt from a scrupulous

cleaning. The Osmia dusts them, brushes them thoroughly with her tarsi

and then sweeps them out backwards. What does she pick up? Not a thing.

It makes no difference: as a conscientious housewife, she gives the

place a touch of the broom nevertheless.

Now for the provisions and the partition-walls. Here the order of the

work changes according to the diameter of the cylinder. My glass tubes

vary greatly in dimensions. The largest have an inner width of a dozen

millimetres (Nearly half an inch.--Translator's Note.); the narrowest

measure six or seven. (About a quarter of an inch.--Translator's Note.)

In the latter, if the bottom suit her, the Osmia sets to work bringing

pollen and honey. If the bottom do not suit her, if the sorghum-pith

plug with which I have closed the rear-end of the tube be too irregular

and badly-joined, the Bee coats it with a little mortar. When this

small repair is made, the harvesting begins.

In the wider tubes, the work proceeds quite differently. At the moment

when the Osmia disgorges her honey and especially at the moment when,

with her hind-tarsi, she rubs the pollen-dust from her ventral brush,

she needs a narrow aperture, just big enough to allow of her passage. I

imagine that in a straitened gallery the rubbing of her whole body

against the sides gives the harvester a support for her brushing-work.

In a spacious cylinder this support fails her; and the Osmia starts

with creating one for herself, which she does by narrowing the channel.

Whether it be to facilitate the storing of the victuals or for any

other reason, the fact remains that the Osmia housed in a wide tube

begins with the partitioning.

Her division is made by a dab of clay placed at right angles to the

axis of the cylinder, at a distance from the bottom determined by the

ordinary length of a cell. The wad is not a complete round; it is more

crescent-shaped, leaving a circular space between it and one side of

the tube. Fresh layers are swiftly added to the dab of clay; and soon

the tube is divided by a partition which has a circular opening at the

side of it, a sort of dog-hole through which the Osmia will proceed to

knead the Bee-bread. When the victualling is finished and the egg laid

upon the heap, the whole is closed and the filled-up partition becomes

the bottom of the next cell. Then the same method is repeated, that is

to say, in front of the just completed ceiling a second partition is

built, again with a side-passage, which is stouter, owing to its

distance from the centre, and better able to withstand the numerous

comings and goings of the housewife than a central orifice, deprived of

the direct support of the wall, could hope to be. When this partition

is ready, the provisioning of the second cell is effected; and so on

until the wide cylinder is completely stocked.

The building of this preliminary party-wall, with a narrow, round

dog-hole, for a chamber to which the victuals will not be brought until

later is not restricted to the Three-horned Osmia; it is also

frequently found in the case of the Horned Osmia and of Latreille's

Osmia. Nothing could be prettier than the work of the last-named, who

goes to the plants for her material and fashions a delicate sheet in

which she cuts a graceful arch. The Chinaman partitions his house with

paper screens; Latreille's Osmia divides hers with disks of thin green

cardboard perforated with a serving-hatch which remains until the room

is completely furnished. When we have no glass houses at our disposal,

we can see these little architectural refinements in the reeds of the

hurdles, if we open them at the right season.

By splitting the bramble-stumps in the course of July, we perceive also

that the Three-pronged Osmia notwithstanding her narrow gallery,

follows the same practice as Latreille's Osmia, with a difference. She

does not build a party-wall, which the diameter of the cylinder would

not permit; she confines herself to putting up a frail circular pad of

green putty, as though to limit, before any attempt at harvesting, the

space to be occupied by the Bee-bread, whose depth could not be

calculated afterwards if the insect did not first mark out its


If, in order to see the Osmia's nest as a whole, we split a reed

lengthwise, taking care not to disturb its contents; or, better still,

if we select for examination the string of cells built in a glass tube,

we are forthwith struck by one detail, namely, the uneven distances

between the partitions, which are placed almost at right angles to the

axis of the cylinder. It is these distances which fix the size of the

chambers, which, with a similar base, have different heights and

consequently unequal holding-capacities. The bottom partitions, the

oldest, are farther apart; those of the front part, near the orifice,

are closer together. Moreover, the provisions are plentiful in the

loftier cells, whereas they are niggardly and reduced to one-half or

even one-third in the cells of lesser height. Let me say at once that

the large cells are destined for the females and the small ones for the



Does the insect which stores up provisions proportionate to the needs

of the egg which it is about to lay know beforehand the sex of that

egg? Or is the truth even more paradoxical? What we have to do is to

turn this suspicion into a certainty demonstrated by experiment. And

first let us find out how the sexes are arranged.

It is not possible to ascertain the chronological order of a laying,

except by going to suitably-chosen species. Fortunately there are a few

species in which we do not find this difficulty: these are the Bees who

keep to one gallery and build their cells in storeys. Among the number

are the different inhabitants of the bramble-stumps, notably the

Three-pronged Osmiae, who form an excellent subject for observation,

partly because they are of imposing size--bigger than any other

bramble-dwellers in my neighbourhood--partly because they are so


Let us briefly recall the Osmia's habits. Amid the tangle of a hedge, a

bramble-stalk is selected, still standing, but a mere withered stump.

In this the insect digs a more or less deep tunnel, an easy piece of

work owing to the abundance of soft pith. Provisions are heaped up

right at the bottom of the tunnel and an egg is laid on the surface of

the food: that is the first-born of the family. At a height of some

twelve millimetres (About half an inch.--Translator's Note.), a

partition is fixed. This gives a second storey, which in its turn

receives provisions and an egg, the second in order of primogeniture.

And so it goes on, storey by storey, until the cylinder is full. Then

the thick plug of the same green material of which the partitions are

formed closes the home and keeps out marauders.

In this common cradle, the chronological order of births is perfectly

clear. The first-born of the family is at the bottom of the series; the

last-born is at the top, near the closed door. The others follow from

bottom to top in the same order in which they followed in point of

time. The laying is numbered automatically; each cocoon tells us its

respective age by the place which it occupies.

A number of eggs bordering on fifteen represents the entire family of

an Osmia, and my observations enable me to state that the distribution

of the sexes is not governed by any rule. All that I can say in general

is that the complete series begins with females and nearly always ends

with males. The incomplete series--those which the insect has laid in

various places--can teach us nothing in this respect, for they are only

fragments starting we know not whence; and it is impossible to tell

whether they should be ascribed to the beginning, to the end, or to an

intermediate period of the laying. To sum up: in the laying of the

Three-pronged Osmia, no order governs the succession of the sexes;

only, the series has a marked tendency to begin with females and to

finish with males.

The mother occupies herself at the start with the stronger sex, the

more necessary, the better-gifted, the female sex, to which she devotes

the first flush of her laying and the fullness of her vigour; later,

when she is perhaps already at the end of her strength, she bestows

what remains of her maternal solicitude upon the weaker sex, the

less-gifted, almost negligible male sex. There are, however, other

species where this law becomes absolute, constant and regular.

In order to go more deeply into this curious question I installed some

hives of a new kind on the sunniest walls of my enclosure. They

consisted of stumps of the great reed of the south, open at one end,

closed at the other by the natural knot and gathered into a sort of

enormous pan-pipe, such as Polyphemus might have employed. The

invitation was accepted: Osmiae came in fairly large numbers, to

benefit by the queer installation.

Three Osmiae especially (O. Tricornis, Latr., O. cornuta, Latr., O.

Latreillii, Spin.) gave me splendid results, with reed-stumps arranged

either against the wall of my garden, as I have just said, or near

their customary abode, the huge nests of the Mason-bee of the Sheds.

One of them, the Three-horned Osmia, did better still: as I have

described, she built her nests in my study, as plentifully as I could


We will consult this last, who has furnished me with documents beyond

my fondest hopes, and begin by asking her of how many eggs her average

laying consists. Of the whole heap of colonized tubes in my study, or

else out of doors, in the hurdle-reeds and the pan-pipe appliances, the

best-filled contains fifteen cells, with a free space above the series,

a space showing that the laying is ended, for, if the mother had any

more eggs available, she would have lodged them in the room which she

leaves unoccupied. This string of fifteen appears to be rare; it was

the only one that I found. My attempts at indoor rearing, pursued

during two years with glass tubes or reeds, taught me that the

Three-horned Osmia is not much addicted to long series. As though to

decrease the difficulties of the coming deliverance, she prefers short

galleries, in which only a part of the laying is stacked. We must then

follow the same mother in her migration from one dwelling to the next

if we would obtain a complete census of her family. A spot of colour,

dropped on the Bee's thorax with a paint-brush while she is absorbed in

closing up the mouth of the tunnel, enables us to recognize the Osmia

in her various homes.

In this way, the swarm that resided in my study furnished me, in the

first year, with an average of twelve cells. Next year, the summer

appeared to be more favourable and the average became rather higher,

reaching fifteen. The most numerous laying performed under my eyes, not

in a tube, but in a succession of Snail-shells, reached the figure of

twenty-six. On the other hand, layings of between eight and ten are not

uncommon. Lastly, taking all my records together, the result is that

the family of the Osmia fluctuates roundabout fifteen in number.

I have already spoken of the great differences in size apparent in the

cells of one and the same series. The partitions, at first widely

spaced, draw gradually nearer to one another as they come closer to the

aperture, which implies roomy cells at the back and narrow cells in

front. The contents of these compartments are no less uneven between

one portion and another of the string. Without any exception known to

me, the large cells, those with which the series starts, have more

abundant provisions than the straitened cells with which the series

ends. The heap of honey and pollen in the first is twice or even thrice

as large as that in the second. In the last cells, the most recent in

date, the victuals are but a pinch of pollen, so niggardly in amount

that we wonder what will become of the larva with that meagre ration.

One would think that the Osmia, when nearing the end of the laying,

attaches no importance to her last-born, to whom she doles out space

and food so sparingly. The first-born receive the benefit of her early

enthusiasm: theirs is the well-spread table, theirs the spacious

apartments. The work has begun to pall by the time that the last eggs

are laid; and the last-comers have to put up with a scurvy portion of

food and a tiny corner.

The difference shows itself in another way after the cocoons are spun.

The large cells, those at the back, receive the bulky cocoons; the

small ones, those in front, have cocoons only half or a third as big.

Before opening them and ascertaining the sex of the Osmia inside, let

us wait for the transformation into the perfect insect, which will take

place towards the end of summer. If impatience get the better of us, we

can open them at the end of July or in August. The insect is then in

the nymphal stage; and it is easy, under this form, to distinguish the

two sexes by the length of the antennae, which are larger in the males,

and by the glassy protuberances on the forehead, the sign of the future

armour of the females. Well, the small cocoons, those in the narrow

front cells, with their scanty store of provisions, all belong to

males; the big cocoons, those in the spacious and well-stocked cells at

the back, all belong to females.

The conclusion is definite: the laying of the Three-horned Osmia

consists of two distinct groups, first a group of females and then a

group of males.

With my pan-pipe apparatus displayed on the walls of my enclosure and

with old hurdle-reeds left lying flat out of doors, I obtained the

Horned Osmia in fair quantities. I persuaded Latreille's Osmia to build

her nest in reeds, which she did with a zeal which I was far from

expecting. All that I had to do was to lay some reed-stumps

horizontally within her reach, in the immediate neighbourhood of her

usual haunts, namely, the nests of the Mason-bee of the Sheds. Lastly,

I succeeded without difficulty in making her build her nests in the

privacy of my study, with glass tubes for a house. The result surpassed

my hopes.

With both these Osmiae, the division of the gallery is the same as with

the Three-horned Osmia. At the back are large cells with plentiful

provisions and widely-spaced partitions; in front, small cells, with

scanty provisions and partitions close together. Also, the larger cells

supplied me with big cocoons and females; the smaller cells gave me

little cocoons and males. The conclusion therefore is exactly the same

in the case of all three Osmiae.

These conclusions, as my notes show, apply likewise, in every respect,

to the various species of Mason-bees; and one clear and simple rule

stands out from this collection of facts. Apart from the strange

exception of the Three-pronged Osmia, who mixes the sexes without any

order, the Bees whom I studied and probably a crowd of others produce

first a continuous series of females and then a continuous series of

males, the latter with less provisions and smaller cells. This

distribution of the sexes agrees with what we have long known of the

Hive-bee, who begins her laying with a long sequence of workers, or

sterile females, and ends it with a long sequence of males. The analogy

continues down to the capacity of the cells and the quantities of

provisions. The real females, the Queen-bees, have wax cells

incomparably more spacious than the cells of the males and receive a

much larger amount of food. Everything therefore demonstrates that we

are here in the presence of a general rule.


But does this rule express the whole truth? Is there nothing beyond a

laying in two series? Are the Osmiae, the Chalicodomae and the rest of

them fatally bound by this distribution of the sexes into two distinct

groups, the male group following upon the female group, without any

mixing of the two? Is the mother absolutely powerless to make a change

in this arrangement, should circumstances require it?

The Three-pronged Osmia already shows us that the problem is far from

being solved. In the same bramble-stump, the two sexes occur very

irregularly, as though at random. Why this mixture in the series of

cocoons of a Bee closely related to the Horned Osmia and the

Three-horned Osmia, who stack theirs methodically by separate sexes in

the hollow of a reed? What the Bee of the brambles does cannot her

kinswomen of the reeds do too? Nothing, so far as I know, explains this

fundamental difference in a physiological act of primary importance.

The three Bees belong to the same genus; they resemble one another in

general outline, internal structure and habits; and, with this close

similarity, we suddenly find a strange dissimilarity.

There is just one thing that might possibly arouse a suspicion of the

cause of this irregularity in the Three-pronged Osmia's laying. If I

open a bramble-stump in the winter to examine the Osmia's nest, I find

it impossible, in the vast majority of cases, to distinguish positively

between a female and a male cocoon: the difference in size is so small.

The cells, moreover, have the same capacity: the diameter of the

cylinder is the same throughout and the partitions are almost always

the same distance apart. If I open it in July, the victualling-period,

it is impossible for me to distinguish between the provisions destined

for the males and those destined for the females. The measurement of

the column of honey gives practically the same depth in all the cells.

We find an equal quantity of space and food for both sexes.

This result makes us foresee what a direct examination of the two sexes

in the adult form tells us. The male does not differ materially from

the female in respect of size. If he is a trifle smaller, it is

scarcely noticeable, whereas, in the Horned Osmia and the Three-horned

Osmia, the male is only half or a third the size of the female, as we

have seen from the respective bulk of their cocoons. In the Mason-bee

of the Walls there is also a difference in size, though less


The Three-pronged Osmia has not therefore to trouble about adjusting

the dimensions of the dwelling and the quantity of the food to the sex

of the egg which she is about to lay; the measure is the same from one

end of the series to the other. It does not matter if the sexes

alternate without order: one and all will find what they need, whatever

their position in the row. The two other Osmiae, with their great

disparity in size between the two sexes, have to be careful about the

twofold consideration of board and lodging.

The more I thought about this curious question, the more probable it

appeared to me that the irregular series of the Three-pronged Osmia and

the regular series of the other Osmiae and of the Bees in general were

all traceable to a common law. It seemed to me that the arrangement in

a succession first of females and then of males did not account for

everything. There must be something more. And I was right: that

arrangement in series is only a tiny fraction of the reality, which is

remarkable in a very different way. This is what I am going to prove by


The succession first of females and then of males is not, in fact,

invariable. Thus, the Chalicodoma, whose nests serve for two or three

generations, ALWAYS lays male eggs in the old male cells, which can be

recognized by their lesser capacity, and female eggs in the old female

cells of more spacious dimensions.

This presence of both sexes at a time, even when there are but two

cells free, one spacious and the other small, proves in the plainest

fashion that the regular distribution observed in the complete nests of

recent production is here replaced by an irregular distribution,

harmonizing with the number and holding-capacity of the chambers to be

stocked. The Mason-bee has before her, let me suppose, only five vacant

cells: two larger and three smaller. The total space at her disposal

would do for about a third of the laying. Well, in the two large cells,

she puts females; in the three small cells she puts males.

As we find the same sort of thing in all the old nests, we must needs

admit that the mother knows the sex of the eggs which she is going to

lay, because that egg is placed in a cell of the proper capacity. We

can go further, and admit that the mother alters the order of

succession of the sexes at her pleasure, because her layings, between

one old nest and another, are broken up into small groups of males and

females according to the exigencies of space in the actual nest which

she happens to be occupying.

Here then is the Chalicodoma, when mistress of an old nest of which she

has not the power to alter the arrangement, breaking up her laying into

sections comprising both sexes just as required by the conditions

imposed upon her. She therefore decides the sex of the egg at will,

for, without this prerogative, she could not, in the chambers of the

nest which she owes to chance, deposit unerringly the sex for which

those chambers were originally built; and this happens however small

the number of chambers to be filled.

When the mother herself founds the dwelling, when she lays the first

rows of bricks, the females come first and the males at the finish.

But, when she is in the presence of an old nest, of which she is quite

unable to alter the general arrangement, how is she to make use of a

few vacant rooms, the large and small alike, if the sex of the egg be

already irrevocably fixed? She can only do so by abandoning the

arrangement in two consecutive rows and accommodating her laying to the

varied exigencies of the home. Either she finds it impossible to make

an economical use of the old nest, a theory refuted by the evidence, or

else she determines at will the sex of the egg which she is about to


The Osmiae themselves will furnish the most conclusive evidence on the

latter point. We have seen that these Bees are not generally miners,

who themselves dig out the foundation of their cells. They make use of

the old structures of others, or else of natural retreats, such as

hollow stems, the spirals of empty shells and various hiding-places in

walls, clay or wood. Their work is confined to repairs to the house,

such as partitions and covers. There are plenty of these retreats; and

the insects would always find first-class ones if it thought of going

any distance to look for them. But the Osmia is a stay-at-home: she

returns to her birthplace and clings to it with a patience extremely

difficult to exhaust. It is here, in this little familiar corner, that

she prefers to settle her progeny. But then the apartments are few in

number and of all shapes and sizes. There are long and short ones,

spacious ones and narrow. Short of expatriating herself, a Spartan

course, she has to use them all, from first to last, for she has no

choice. Guided by these considerations, I embarked on the experiments

which I will now describe.

I have said how my study became a populous hive, in which the

Three-horned Osmia built her nests in the various appliances which I

had prepared for her. Among these appliances, tubes, either of glass or

reed, predominated. There were tubes of all lengths and widths. In the

long tubes, entire or almost entire layings, with a series of females

followed by a series of males, were deposited. As I have already

referred to this result, I will not discuss it again. The short tubes

were sufficiently varied in length to lodge one or other portion of the

total laying. Basing my calculations on the respective lengths of the

cocoons of the two sexes, on the thickness of the partitions and the

final lid, I shortened some of these to the exact dimensions required

for two cocoons only, of different sexes.

Well, these short tubes, whether of glass or reed, were seized upon as

eagerly as the long tubes. Moreover, they yielded this splendid result:

their contents, only a part of the total laying, always began with

female and ended with male cocoons. This order was invariable; what

varied was the number of cells in the long tubes and the proportion

between the two sorts of cocoons, sometimes males predominating and

sometimes females.

When confronted with tubes too small to receive all her family, the

Osmia is in the same plight as the Mason-bee in the presence of an old

nest. She thereupon acts exactly as the Chalicodoma does. She breaks up

her laying, divides it into series as short as the room at her disposal

demands; and each series begins with females and ends with males. This

breaking up, on the one hand, into sections in all of which both sexes

are represented and the division, on the other hand, of the entire

laying into just two groups, one female, the other male, when the

length of the tube permits, surely provide us with ample evidence of

the insect's power to regulate the sex of the egg according to the

exigencies of space.

And besides the exigencies of space one might perhaps venture to add

those connected with the earlier development of the males. These burst

their cocoons a couple of weeks or more before the females; they are

the first who hasten to the sweets of the almond-tree. In order to

release themselves and emerge into the glad sunlight without disturbing

the string of cocoons wherein their sisters are still sleeping, they

must occupy the upper end of the row; and this, no doubt, is the reason

that makes the Osmia end each of her broken layings with males. Being

next to the door, these impatient ones will leave the home without

upsetting the shells that are slower in hatching.

I had offered at the same time to the Osmiae in my study some old nests

of the Mason-bee of the Shrubs, which are clay spheroids with

cylindrical cavities in them. These cavities are formed, as in the old

nests of the Mason-bee of the Pebbles, of the cell properly so-called

and of the exit-way which the perfect insect cut through the outer

coating at the time of its deliverance. The diameter is about 7

millimetres (.273 inch.--Translator's Note.); their depth at the centre

of the heap is 23 millimetres (.897 inch.--Translator's Note.) and at

the edge averages 14 millimetres. (.546 inch.--Translator's Note.)

The deep central cells receive only the females of the Osmia; sometimes

even the two sexes together, with a partition in the middle, the female

occupying the lower and the male the upper storey. Lastly, the deeper

cavities on the circumference are allotted to females and the shallower

to males.

We know that the Three-horned Osmia prefers to haunt the habitations of

the Bees who nidify in populous colonies, such as the Mason-bee of the

Sheds and the Hairy-footed Anthophora, in whose nests I have noted

similar facts.

Thus the sex of the egg is optional. The choice rests with the mother,

who is guided by considerations of space and, according to the

accommodation at her disposal, which is frequently fortuitous and

incapable of modification, places a female in this cell and a male in

that, so that both may have a dwelling of a size suited to their

unequal development. This is the unimpeachable evidence of the numerous

and varied facts which I have set forth. People unfamiliar with insect

anatomy--the public for whom I write--would probably give the following

explanation of this marvellous prerogative of the Bee: the mother has

at her disposal a certain number of eggs, some of which are irrevocably

female and the others irrevocably male: she is able to pick out of

either group the one which she wants at the actual moment; and her

choice is decided by the holding capacity of the cell that has to be

stocked. Everything would then be limited to a judicious selection from

the heap of eggs.

Should this idea occur to him, the reader must hasten to reject it.

Nothing could be more false, as the most casual reference to anatomy

will show. The female reproductive apparatus of the Hymenoptera

consists generally of six ovarian tubes, something like glove-fingers,

divided into bunches of three and ending in a common canal, the

oviduct, which carries the eggs outside. Each of these glove-fingers is

fairly wide at the base, but tapers sharply towards the tip, which is

closed. It contains, arranged in a row, one after the other, like beads

on a string, a certain number of eggs, five or six for instance, of

which the lower ones are more or less developed, the middle ones

halfway towards maturity, and the upper ones very rudimentary. Every

stage of evolution is here represented, distributed regularly from

bottom to top, from the verge of maturity to the vague outlines of the

embryo. The sheath clasps its string of ovules so closely that any

inversion of the order is impossible. Besides, an inversion would

result in a gross absurdity: the replacing of a riper egg by another in

an earlier stage of development.

Therefore, in each ovarian tube, in each glove-finger, the emergence of

the eggs occurs according to the order governing their arrangement in

the common sheath; and any other sequence is absolutely impossible.

Moreover, at the nesting-period, the six ovarian sheaths, one by one

and each in its turn, have at their base an egg which in a very short

time swells enormously. Some hours or even a day before the laying,

that egg by itself represents or even exceeds in bulk the whole of the

ovigerous apparatus. This is the egg which is on the point of being

laid. It is about to descend into the oviduct, in its proper order, at

its proper time; and the mother has no power to make another take its

place. It is this egg, necessarily this egg and no other, that will

presently be laid upon the provisions, whether these be a mess of honey

or a live prey; it alone is ripe, it alone lies at the entrance to the

oviduct; none of the others, since they are farther back in the row and

not at the right stage of development, can be substituted at this

crisis. Its birth is inevitable.

What will it yield, a male or a female? No lodging has been prepared,

no food collected for it; and yet both food and lodging have to be in

keeping with the sex that will proceed from it. And here is a much more

puzzling condition: the sex of that egg, whose advent is predestined,

has to correspond with the space which the mother happens to have found

for a cell. There is therefore no room for hesitation, strange though

the statement may appear: the egg, as it descends from its ovarian

tube, has no determined sex. It is perhaps during the few hours of its

rapid development at the base of its ovarian sheath, it is perhaps on

its passage through the oviduct that it receives, at the mother's

pleasure, the final impress that will produce, to match the cradle

which it has to fill, either a female or a male.


Thereupon the following question presents itself. Let us admit that,

when the normal conditions remain, a laying would have yielded m

females and n males. Then, if my conclusions are correct, it must be in

the mother's power, when the conditions are different, to take from the

m group and increase the n group to the same extent; it must be

possible for her laying to be represented as m - 1, m - 2, m - 3, etc.

females and by n + 1, n + 2, n + 3, etc. males, the sum of m + n

remaining constant, but one of the sexes being partly permuted into the

other. The ultimate conclusion even cannot be disregarded: we must

admit a set of eggs represented by m - m, or zero, females and of n + m

males, one of the sexes being completely replaced by the other.

Conversely, it must be possible for the feminine series to be augmented

from the masculine series to the extent of absorbing it entirely. It

was to solve this question and some others connected with it that I

undertook, for the second time, to rear the Three-horned Osmia in my


The problem on this occasion is a more delicate one; but I am also

better-equipped. My apparatus consists of two small closed

packing-cases, with the front side of each pierced with forty holes, in

which I can insert my glass tubes and keep them in a horizontal

position. I thus obtain for the Bees the darkness and mystery which

suit their work and for myself the power of withdrawing from my hive,

at any time, any tube that I wish, with the Osmia inside, so as to

carry it to the light and follow, if need be with the aid of the lens,

the operations of the busy worker. My investigations, however frequent

and minute, in no way hinder the peaceable Bee, who remains absorbed in

her maternal duties.

I mark a plentiful number of my guests with a variety of dots on the

thorax, which enables me to follow any one Osmia from the beginning to

the end of her laying. The tubes and their respective holes are

numbered; a list, always lying open on my desk, enables me to note from

day to day, sometimes from hour to hour, what happens in each tube and

particularly the actions of the Osmiae whose backs bear distinguishing

marks. As soon as one tube is filled, I replace it by another.

Moreover, I have scattered in front of either hive a few handfuls of

empty Snail-shells, specially chosen for the object which I have in

view. Reasons which I will explain later led me to prefer the shells of

Helix caespitum. Each of the shells, as and when stocked, received the

date of the laying and the alphabetical sign corresponding with the

Osmia to whom it belonged. In this way, I spent five or six weeks in

continual observation. To succeed in an enquiry, the first and foremost

condition is patience. This condition I fulfilled; and it was rewarded

with the success which I was justified in expecting.

The tubes employed are of two kinds. The first, which are cylindrical

and of the same width throughout, will be of use for confirming the

facts observed in the first year of my experiments in indoor rearing.

The others, the majority, consist of two cylinders which are of very

different diameters, set end to end. The front cylinder, the one which

projects a little way outside the hive and forms the entrance-hole,

varies in width between 8 and 12 millimetres. (Between .312 and .468

inch.--Translator's Note.) The second, the back one, contained entirely

within my packing-case, is closed at its far end and is 5 to 6

millimetres in diameter. (.195 to .234 inch.--Translator's Note.) Each

of the two parts of the double-galleried tunnel, one narrow and one

wide, measures at most a decimetre in length. (3.9

inches.--Translator's Note.) I thought it advisable to have these short

tubes, as the Osmia is thus compelled to select different lodgings,

each of them being insufficient in itself to accommodate the total

laying. In this way I shall obtain a greater variety in the

distribution of the sexes. Lastly, at the mouth of each tube, which

projects slightly outside the case, there is a little paper tongue,

forming a sort of perch on which the Osmia alights on her arrival and

giving easy access to the house. With these facilities, the swarm

colonized fifty-two double-galleried tubes, thirty-seven cylindrical

tubes, seventy-eight Snail-shells and a few old nests of the Mason-bee

of the Shrubs. From this rich mine of material I will take what I want

to prove my case.

Every series, even when incomplete, begins with females and ends with

males. To this rule I have not yet found an exception, at least in

galleries of normal diameter. In each new abode the mother busies

herself first of all with the more important sex. Bearing this point in

mind, would it be possible for me, by manoeuvring, to obtain an

inversion of this order and make the laying begin with males? I think

so, from the results already ascertained and the irresistible

conclusions to be drawn from them. The double-galleried tubes are

installed in order to put my conjectures to the proof.

The back gallery, 5 or 6 millimetres wide (.195 to .234

inch.--Translator's Note.), is too narrow to serve as a lodging for

normally developed females. If, therefore, the Osmia, who is very

economical of her space, wishes to occupy them, she will be obliged to

establish males there. And her laying must necessarily begin here,

because this corner is the rear-most part of the tube. The foremost

gallery is wide, with an entrance-door on the front of the hive. Here,

finding the conditions to which she is accustomed, the mother will go

on with her laying in the order which she prefers.

Let us now see what has happened. Of the fifty-two double-galleried

tubes, about a third did not have their narrow passage colonized. The

Osmia closed its aperture communicating with the large passage; and the

latter alone received the eggs. This waste of space was inevitable. The

female Osmiae, though nearly always larger than the males, present

marked differences among one another: some are bigger, some are

smaller. I had to adjust the width of the narrow galleries to Bees of

average dimensions. It may happen therefore that a gallery is too small

to admit the large-sized mothers to whom chance allots it. When the

Osmia is unable to enter the tube, obviously she will not colonize it.

She then closes the entrance to this space which she cannot use and

does her laying beyond it, in the wide tube. Had I tried to avoid these

useless apparatus by choosing tubes of larger calibre, I should have

encountered another drawback: the medium-sized mothers, finding

themselves almost comfortable, would have decided to lodge females

there. I had to be prepared for it: as each mother selected her house

at will and as I was unable to interfere in her choice, a narrow tube

would be colonized or not, according as the Osmia who owned it was or

was not able to make her way inside.

There remain some forty pairs of tubes with both galleries colonized.

In these there are two things to take into consideration. The narrow

rear tubes of 5 or 5 1/2 millimetres (.195 to .214 inch.--Translator's

Note.)--and these are the most numerous--contain males and males only,

but in short series, between one and five. The mother is here so much

hampered in her work that they are rarely occupied from end to end; the

Osmia seems in a hurry to leave them and to go and colonize the front

tube, whose ample space will leave her the liberty of movement

necessary for her operations. The other rear tubes, the minority, whose

diameter is about 6 millimetres (.234 inch.--Translator's Note.),

contain sometimes only females and sometimes females at the back and

males towards the opening. One can see that a tube a trifle wider and a

mother slightly smaller would account for this difference in the

results. Nevertheless, as the necessary space for a female is barely

provided in this case, we see that the mother avoids as far as she can

a two-sex arrangement beginning with males and that she adopts it only

in the last extremity. Finally, whatever the contents of the small tube

may be, those of the large one, following upon it, never vary and

consist of females at the back and males in front.

Though incomplete, because of circumstances very difficult to control,

the result of the experiment is none the less very remarkable.

Twenty-five apparatus contain only males in their narrow gallery, in

numbers varying from a minimum of one to a maximum of five. After these

comes the colony of the large gallery, beginning with females and

ending with males. And the layings in these apparatus do not always

belong to late summer or even to the intermediate period: a few small

tubes contain the earliest eggs of the entire swarm. A couple of

Osmiae, more forward than the others, set to work on the 23rd of April.

Both of them started their laying by placing males in the narrow tubes.

The meagre supply of provisions was enough in itself to show the sex,

which proved later to be in accordance with my anticipations. We see

then that, by my artifices, the whole swarm starts with the converse of

the normal order. This inversion is continued, at no matter what

period, from the beginning to the end of the operations. The series

which, according to rule, would begin with females now begins with

males. Once the larger gallery is reached, the laying is pursued in the

usual order.

We have advanced one step and that no small one: we have seen that the

Osmia, when circumstances require it, is capable of reversing the

sequence of the sexes. Would it be possible, provided that the tube

were long enough, to obtain a complete inversion, in which the entire

series of the males should occupy the narrow gallery at the back and

the entire series of the females the roomy gallery in front? I think

not; and I will tell you why.

Long and narrow cylinders are by no means to the Osmia's taste, not

because of their narrowness but because of their length. Observe that

for each load of honey brought the worker is obliged to move backwards

twice. She enters, head first, to begin by disgorging the honey-syrup

from her crop. Unable to turn in a passage which she blocks entirely,

she goes out backwards, crawling rather than walking, a laborious

performance on the polished surface of the glass and a performance

which, with any other surface, would still be very awkward, as the

wings are bound to rub against the wall with their free end and are

liable to get rumpled or bent. She goes out backwards, reaches the

outside, turns round and goes in again, but this time the opposite way,

so as to brush off the load of pollen from her abdomen on to the heap.

If the gallery is at all long, this crawling backwards becomes

troublesome after a time; and the Osmia soon abandons a passage that is

too small to allow of free movement. I have said that the narrow tubes

of my apparatus are, for the most part, only very incompletely

colonized. The Bee, after lodging a small number of males in them,

hastens to leave them. In the wide front gallery she can stay where she

is and still be able to turn round easily for her different

manipulations; she will avoid those two long journeys backwards, which

are so exhausting and so bad for her wings.

Another reason no doubt prompts her not to make too great a use of the

narrow passage, in which she would establish males, followed by females

in the part where the gallery widens. The males have to leave their

cells a couple of weeks or more before the females. If they occupy the

back of the house they will die prisoners or else they will overturn

everything on their way out. This risk is avoided by the order which

the Osmia adopts.

In my tubes, with their unusual arrangement, the mother might well find

the dilemma perplexing: there is the narrowness of the space at her

disposal and there is the emergence later on. In the narrow tubes, the

width is insufficient for the females; on the other hand, if she lodges

males there, they are liable to perish, since they will be prevented

from issuing at the proper moment. This would perhaps explain the

mother's hesitation and her obstinacy in settling females in some of my

apparatus which looked as if they could suit none but males.

A suspicion occurs to me, a suspicion aroused by my attentive

examination of the narrow tubes. All, whatever the number of their

inmates, are carefully plugged at the opening, just as separate tubes

would be. It might therefore be the case that the narrow gallery at the

back was looked upon by the Osmia not as the prolongation of the large

front gallery, but as an independent tube. The facility with which the

worker turns as soon as she reaches the wide tube, her liberty of

action, which is now as great as in a doorway communicating with the

outer air, might well be misleading and cause the Osmia to treat the

narrow passage at the back as though the wide passage in front did not

exist. This would account for the placing of the female in the large

tube above the males in the small tube, an arrangement contrary to her


I will not undertake to decide whether the mother really appreciates

the danger of my snares, or whether she makes a mistake in considering

only the space at her disposal and beginning with males, who are liable

to remain imprisoned. At any rate, I perceive a tendency to deviate as

little as possible from the order which safeguards the emergence of

both sexes. This tendency is demonstrated by her repugnance to

colonizing my narrow tubes with long series of males. However, so far

as we are concerned, it does not matter much what passes at such times

in the Osmia's little brain. Enough for us to know that she dislikes

narrow and long tubes, not because they are narrow, but because they

are at the same time long.

And, in fact, she does very well with a short tube of the same

diameter. Such are the cells in the old nests of the Mason-bee of the

Shrubs and the empty shells of the Garden Snail. With the short tube

the two disadvantages of the long tube are avoided. She has very little

of that crawling backwards to do when she has a Snail-shell for the

home of her eggs and scarcely any when the home is the cell of the

Mason-bee. Moreover, as the stack of cocoons numbers two or three at

most, the deliverance will be exempt from the difficulties attached to

a long series. To persuade the Osmia to nidify in a single tube long

enough to receive the whole of her laying and at the same time narrow

enough to leave her only just the possibility of admittance appears to

me a project without the slightest chance of success: the Bee would

stubbornly refuse such a dwelling or would content herself with

entrusting only a very small portion of her eggs to it. On the other

hand, with narrow but short cavities, success, without being easy,

seems to me at least quite possible. Guided by these considerations, I

embarked upon the most arduous part of my problem: to obtain the

complete or almost complete permutation of one sex with the other; to

produce a laying consisting only of males by offering the mother a

series of lodgings suited only to males.

Let us in the first place consult the old nests of the Mason-bee of the

Shrubs. I have said that these mortar spheroids, pierced all over with

little cylindrical cavities, are a adopted pretty eagerly by the

Three-horned Osmia, who colonizes them before my eyes with females in

the deep cells and males in the shallow cells. That is how things go

when the old nest remains in its natural state. With a grater, however,

I scrape the outside of another nest so as to reduce the depth of the

cavities to some ten millimetres. (About two-fifths of an

inch.--Translator's Note.) This leaves in each cell just room for one

cocoon, surmounted by the closing stopper. Of the fourteen cavities in

the nests, I leave two intact, measuring fifteen millimetres in depth.

(.585 inch.--Translator's Note.) Nothing could be more striking than

the result of this experiment, made in the first year of my home

rearing. The twelve cavities whose depth had been reduced all received

males; the two cavities left untouched received females.

A year passes and I repeat the experiment with a nest of fifteen cells;

but this time all the cells are reduced to the minimum depth with the

grater. Well, the fifteen cells, from first to last, are occupied by

males. It must be quite understood that, in each case, all the

offspring belonged to one mother, marked with her distinguishing dot

and kept in sight as long as her laying lasted. He would indeed be

difficult to please who refused to bow before the results of these two

experiments. If, however, he is not yet convinced, here is something to

remove his last doubts.

The Three-horned Osmia often settles her family in old shells,

especially those of the Common Snail (Helix aspersa), who is so common

under the stone-heaps and in the crevices of the little unmortared

walls that support our terraces. In this species the spiral is wide

open, so that the Osmia, penetrating as far down as the helical passage

permits, finds, immediately above the point which is too narrow to

pass, the space necessary for the cell of a female. This cell is

succeeded by others, wider still, always for females, arranged in a

line in the same way as in a straight tube. In the last whorl of the

spiral, the diameter would be too great for a single row. Then

longitudinal partitions are added to the transverse partitions, the

whole resulting in cells of unequal dimensions in which males

predominate, mixed with a few females in the lower storeys. The

sequence of the sexes is therefore what it would be in a straight tube

and especially in a tube with a wide bore, where the partitioning is

complicated by subdivisions on the same level. A single Snail-shell

contains room for six or eight cells. A large, rough earthen stopper

finishes the nest at the entrance to the shell.

As a dwelling of this sort could show us nothing new, I chose for my

swarm the Garden Snail (Helix caespitum), whose shell, shaped like a

small swollen Ammonite, widens by slow degrees, the diameter of the

usable portion, right up to the mouth, being hardly greater than that

required by a male Osmia-cocoon. Moreover, the widest part, in which a

female might find room, has to receive a thick stopping-plug, below

which there will often be a free space. Under all these conditions, the

house will hardly suit any but males arranged one after the other.

The collection of shells placed at the foot of each hive includes

specimens of different sizes. The smallest are 18 millimetres (.7

inch.--Translator's Note.) in diameter and the lar